The tolerance and enrichment transport of zinc in Iris ensata under zinc stress

In this study, we investigated the zinc (Zn) tolerance, enrichment, and translocation characteristics of Iris ensata under five different Zn stresses using a soil culture method. The results revealed gradual reductions in the biomass, plant height, leaf width, and leaf area of I. ensata exposed to increasing Zn concentrations, whereas the root-crown ratio and root length showed trends characterized by an initial increase followed by a subsequent reduction, and an initial reduction followed by an increase and then a subsequent decline, respectively. Net photosynthetic rate, transpiration rate, and stomatal conductance showed similar declining trends with increasing Zn concentrations, whereas intercellular carbon dioxide concentrations gradually increased with significant differences among treatments (P < 0.05). Total chlorophyll and chlorophyll a content, along with the chlorophyll a/b ratio declined with increasing Zn concentrations, whereas the highest content of chlorophyll b was detected at a Zn concentration of 200 mg·kg⁻¹ and gradually declined at higher Zn concentrations. The activity of superoxide dismutase increased with increasing Zn concentrations, whereas that of peroxidase initially increased and subsequently declined, and the activity of catalase was highest at 1 000 mg·kg⁻¹ and lowest at 2 000 mg·kg⁻¹. In response to different levels of Zn contamination, the enrichment of Zn in I. ensata showed an increasing trend with increasing concentration, with enrichment in the below-ground parts being consistently higher than that in the above-ground parts. The peak uptake was reached at 2 000 mg·kg⁻¹, with a total enrichment of 15 844.44 mg·kg⁻¹ and a transit factor of 0.733. The results of subcellular distribution revealed that Zn was mainly distributed in the cell walls and soluble material. Collectively, our findings indicate that I. ensata planted in soils with Zn concentrations of between 200 and 2 000 mg·kg⁻¹ was influenced to different degrees, which can provide a theoretical basis for future garden applications.